1. Field of the Invention
The present invention relates to a recording method and apparatus such as an ink jet recording apparatus or a thermal recording apparatus which forms images by driving a recording head having a plurality of recording elements.
More specifically, the present invention relates to a recording method and apparatus which is preferably applicable to apparatuses using as recording elements, thermal elements having thermal resistors and electrodes connected to the thermal resistors. One of those apparatuses is an ink jet recording apparatus that has thermal elements disposed in liquid passages, and ink ejection outlets disposed on the surface of the recording head and communicating to the liquid passages.
2. Description of the Prior Art
Recently, the ink jet recording method has been increasingly attracting attention. This is because of its various advantages which are conventionally known: noise during recording is very low; color recording can be easily achieved by this technique; and recording to common paper can be carried out.
Above all, an ink jet recording apparatus which uses thermal energy for recording attracts particular attention because its size can be easily reduced, and the high density alignment of the ink ejection outlets is possible. The ink jet recording apparatus performs recording as follows: thermal elements provided in the liquid passages communicate to minute ink ejection outlets from which ink is ejected and heated by electric currents; and the ink is ejected from the ejection outlets in the form of ink droplets by using the sudden volume change involved in the bubbling of the ink around the thermal elements, which is caused by heating.
In this type of ink jet recording apparatus using thermal energy, the recording head is usually provided with a plurality of ink ejection outlets which are integrally aligned in a certain direction. For example, a so-called full line type recording head in which the ink ejection outlets are aligned over the full length across the width of a recording medium such as a sheet of paper, an OHP sheet or a sheet of cloth, the thermal elements are driven all at once, or block by block consisting of a certain number of the thermal elements by applying voltage pulses of a certain width in sequence. In general, it is important to control the pulse width so that each pulse gives just sufficient thermal energy for ejecting ink so that excess thermal energy is not produced. This is important not only for energy saving but also for stabilizing the ink ejection in the course of the repetitive drive of the recording head. Such a driving technique is also used by the recording head of a thermal recording apparatus.
The resistances of the thermal elements laminated on a substrate, however, are not uniform. As a result, amounts of heat generation of the thermal elements vary according to the variation in resistances of the thermal elements. This causes the volume change of the ink at bubbling to vary for respective thermal elements, the quantity of ejected ink to vary, thereby making the diameters of dots different, which will deteriorate the quality of recorded images. This problem holds true of other recording apparatus such as a thermal recording apparatus .
Furthermore, in conventional ink jet recording apparatuses or thermal recording apparatuses, all the thermal elements in the head are driven by pulses of the same width having the same drive voltage. This presents a problem that not all the thermal elements are driven by the optimum drive condition: to some thermal elements, more than sufficient energy is applied, thereby shortening the life of the thermal elements; whereas, to other elements, less than necessary energy is applied, thereby destabilizing the ejection of the ink by the thermal elements.
Moreover, in a recording head which is provided with a number of ink ejection outlets aligned in the direction of printing, for example, as in a recording head of a so-called full-multi-type recording head in which the ink ejection outlets are aligned over the full length across the recording paper, the variation in the resistances of the thermal elements further increases, which presents a problem that the stability of the ink ejection is further deteriorated.